The manufacture and operation of many objects is a function of the object's temperature. Where an object is formed of material that poorly conducts heat, as in the case of an elastomeric containing object such as a conventional pneumatic tire, the behavior of the object is generally a function of its internal temperature. Unfortunately it has often not heretofore been possible to directly and accurately ascertain such an object's internal temperature, particularly both during the object's manufacture and actual operation. As a result, control of the manufacturing process has not been as precise and certain as desired. Moreover, it has not been possible to collect data precisely reflective of the object's operational performance and characteristics.
With regard to conventional pneumatic tires, it is well known that an improperly cured tire may result in an unusable product. It thus becomes imperative to obtain accurate knowledge of the instantaneous internal temperature of such objects both during manufacture and operation.
All techniques for monitoring the temperature of elastomeric containing objects, such as tires may be broadly said to fall into two categories, those where measurements are made external to the tire and those where measurements are made internal of the tire. Since elastomeric materials are poor thermal conductors, a measurement of the external surface temperature of a tire will not be equal to and will not necessarily accurately reflect the internal tire temperature. Nevertheless, external measurement techniques (such as the use of infrared sensors and thermocouple transducers coupled to the tire surface) are popular because they are nondestructive, leaving the tire in an otherwise usable condition after the temperature testing process is complete, and may be utilized to monitor tire temperature when the tire is mounted and in actual use. Moreover, models have been developed to predict internal temperatures during curing of a tire where conventional thermal conduction curing is employed.
Presently known internal measurement techniques consist of the insertion of a transducer (as a thermocouple or needle pyrometer) directly into the interior of the tire at one or more preselected regions of interest. Although more accurate than externally obtained measurements, the insertion of a transducer into the tire generates its own heat as a result of friction, inducing a transient error in any obtained temperature measurement. Of course, the mechanical process of inserting a transducer into the interior of a tire takes time and often, if not virtually always, results in the destruction of the tire. Accordingly, this type of temperature measurement is economically wasteful, may be made only on a representative sampling of tires in production, and even then necessitates an interruption in the manufacturing routine.
As energy and labor costs have increased, manufacturers of tires have been attracted to the utilization of microwave frequency radiation to induce heating in tires. However, the nature of a microwave frequency electromagnetic field precludes the use of metallic transducers as thermocouples and needle pyrometers for temperature measurements. Since accurate models to predict, from external surface temperatures, the internal tire temperatures during curing induced with microwave frequency radiation are not known, one is presently incapable of accurately monitoring the temperature of a tire whose cure was induced with microwave frequency radiation, thus significantly retarding the growth of this curing technique. This lack of accurate knowledge as to the instantaneous internal temperature of tires whose cure is induced with microwave frequency radiation has caused manufacturers to limit the use of microwave frequency radiation to "preheating" tires to where their internal temperature is raised to a range where curing by conventional means may take place.
The use of electroacoustics for the determination of distance is well-known in many endeavors. Relying on the principle that for a constant temperature and pressure sound travels through a material at a substantially constant velocity (although this velocity differs for different materials), electroacoustic frequency (such as ultrasonic) pulses are generated and propogated through the material of interest, whereupon the distance the pulse traveled may be calculated by multiplying its velocity times the pulse propogation time. Implementing this technique, many devices are commercially available to determine the depth of bodies of water and any fish therein, to determine the profile of three dimensional objects hidden within other objects (as a fetus developing within its mother's body), and to determine the thickness of strips of materials, to name a few applications.
Heretofore, to my knowledge, no one has contemplated utilization of a change in the velocity of sound to determine temperature. In all instances of which I am aware, I have found that, over a typical working range of temperatures for curing of elastomeric containing materials or compounds, the velocity of sound therethrough varies substantially linearly with temperature. By measuring the time it takes an ultrasonic pulse to propogate through a reference tire at least at two different measured, internal temperatures, the method I have invented permits the continuous and nondestructive monitoring of internal temperature for all similar tires. Additionally, the method I have developed eliminates variations in ultrasonic pulse propogation times as a result of variations in tire thickness, permitting the continuous and nondestructive monitoring of internal temperature for any object having the same material as that of the reference tire material.